In fuel cell powerplants requiring steam, such as those incorporating a steam reformer for converting a hydrocarbon fuel to hydrogen, the steam is typically provided by utilizing high grade waste heat, such as heat generated in the fuel cells. Commonly a boiler is used as part of a process to produce the steam. Two patents which describe fuel cell powerplants having integrated steam reforming reactors and boilers for producing the steam for the reactors are commonly owned U.S. Pat. Nos. 4,001,041 and 4,004,947. The heat for creating the steam in the boiler is provided by heated water and steam within a two phase coolant loop which is circulated in indirect heat exchange relation with the boiler and the fuel cell stack.
In U.S. Pat. Nos. 4,072,625 and 4,238,403, 10 to 30% of the steam for a reactor is produced by humidifying the gas stream in a saturator. In the saturator a dry hydrocarbon is passed into direct contact with a circulating stream of liquid water heated by low grade waste heat and picks up the water evaporated therefrom. A boiler provides the balance of the steam for those systems; and the pressure in the steam reform reactor is limited by the pressure at which steam can be raised in the boiler through an indirect heat exchange process.
Commonly owned U.S. Pat. No. 3,677,823 describes a fuel cell powerplant which also includes a boiler to produce at least part of the steam for a steam reforming reactor, the heat for the boiler being provided by the exhaust from the reactor burner. The remainder of the steam is provided by humidifying the fuel in a saturator. In the saturator water and the fuel gas are heated together through a heat exchanger wall.
Commonly owned U.S. Pat. No. 4,333,992 describes a molten carbonate fuel cell powerplant including a steam reformer for producing the hydrogen fuel for the fuel cells. Water for the steam reformer is condensed from the anode exhaust gases of the cell and reduced in pressure by throttling across a valve. The heat from the anode exhaust, prior to the water being condensed therefrom, and the heat of condensation is used to boil the condensed water to produce steam. The steam is raised at a lower pressure than that at which the water is condensed. Both the pressure and temperature in the boiler are lower than the saturation pressure and temperature in the condenser. The steam must then be increased back to system pressure, such as by a series of compressors driven by a motor or a source of waste energy from the powerplant.
Other U.S. Patents describing fuel cells and fuel cell systems which involve reforming hydrocarbon fuels are U.S. Pat. Nos. 3,539,395; 3,453,146; and 3,544,374.